Fuel cells are power generation systems that convert chemical energy of a fuel into electrical energy by an electrochemical reaction in a stack without converting the chemical energy into heat by combustion.
Such a fuel cell may not only supply electric power for industrial use, domestic use and vehicle driving, but also be applied to power supply of small electric/electronic products, especially portable devices.
Currently, a polymer electrolyte membrane fuel cell (PEMFC), also known as a proton exchange membrane fuel cell, is used as a power source for vehicle driving.
The PEMFC has a lower operating temperature, higher efficiency, higher current density and output density, shorter startup time, and faster response to load change than other types of fuel cells, and is thus widely usable as a power source for portable devices.
The PEMFC includes a membrane electrode assembly (MEA) formed by attaching catalyst electrode layers, on which an electrochemical reaction occurs, to both sides of a polymer electrolyte membrane, through which hydrogen ions are moved, a gas diffusion layer (GDL) serving to distribute the reaction gases evenly and transfer the generated electric energy, a gasket and a fastening mechanism for maintaining airtightness of the reaction gases and the cooling water and a proper fastening pressure, and a bipolar plate for moving the reaction gases and the cooling water.
Further, a fuel cell system applied to a fuel cell vehicle includes a fuel cell stack for generating electrical energy from an electrochemical reaction of reaction gases (hydrogen as a fuel and oxygen as an oxidizer), a hydrogen supply apparatus for supplying hydrogen to the fuel cell stack as a fuel, an air supply apparatus for supplying air containing oxygen to the fuel cell stack, a heat and water management system for controlling the operation temperature of the fuel cell stack and performing a water management function, and a fuel cell controller for controlling the overall operation of the fuel cell system.
In a typical fuel cell system, the hydrogen supply apparatus includes a hydrogen storage (hydrogen tank), a regulator, a hydrogen pressure control valve, and a hydrogen recirculation device, and the air supply apparatus includes an air blower and a humidifier. The heat and water management system includes a coolant pump, a water tank, and a radiator.
FIG. 1 illustrates a procedure of fabricating a typical GDL-MEA assembly. As shown in FIG. 1, a membrane electrode assembly (MEA) is fabricated by forming electrodes (cathode, anode) on both surfaces of an electrolyte membrane and then attaching sub gasket films.
The MEA prepared in this way is subjected to heat treatment through thermocompression to enhance durability. The heat-treated MEA has a high durability but exhibits degraded performance due to deterioration thereof.
As shown in FIG. 1, gas diffusion layers (GDLs) are bonded to both sides of the completed MEA. The body obtained through bonding as shown in FIG. 1 is referred to as a GDL-MEA assembly. Bonding methods for GDL-MEA include using thermocompression and using an adhesive. However, thermocompression bonding may not be applicable depending on the material or process of the MEA. When an adhesive is used, product yield is problematic.